While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration densities and operating speeds in LSI devices, the DUV lithography is studied as the advanced microfabrication technology. In particular, the photolithography using a KrF or ArF excimer laser as the energy source is developed and implemented as an essential technique capable of micropatterning to a feature size of 0.3 μm or less.
The chemically amplified resist materials for use in photolithography using light of an excimer laser, especially KrF excimer laser having a wavelength of 253 nm and ArF excimer laser having a wavelength of 193 nm, are required as a matter of course to have a high transmittance to light of the relevant wavelength. In addition, they are required to have an etch resistance sufficient to allow for film thickness reduction, a high sensitivity sufficient to eliminate any extra burden on the expensive optical material, and especially, a high resolution sufficient to form a fine pattern in a precise manner. A base resin having a high transparency, rigidity and reactivity must be developed before these requirements can be met. Active efforts were made to develop such resins, with some fruitful results. While studies are currently made on the ArF immersion, EUV and EB lithography processes to enable further miniaturization, the resin is required to have a higher resolution as well. In the advanced resist materials comprising many components of complex structure including a base resin, certain chemical reactions can take place during shelf storage due to interaction between components. Often the base resin, acid generator or surfactant will be decomposed, indicating a loss of shelf stability. It would thus be desirable to have a resist material which meets both high resolution and shelf stability for fine pattern formation and which is applicable to the immersion lithography without a need for protective film.
For the purpose of improving the resolution of a chemically amplified resist material to be processed by excimer laser photolithography, especially in the case of patterning to a ultrafine size of 0.1 μm or less, it is very important to control the diffusion of acid generated by an acid generator in the exposed area. In general, as the pattern size is reduced, the optimum acid diffusion rate is also reduced. For the advanced chemically amplified resist materials, it is a common practice to add an acid diffusion controlling agent, known as quencher, thereto for sensitivity adjustment, resolution enhancement or other purposes. Typically, amine compounds are used as the quencher. For optimum adjustment of the diffusion rate of generated acid, the structure of a quencher and a combination of the quencher with an acid generator anion species are crucial.
As the quencher having an excellent acid diffusion control function, Patent Document 1 proposes an amine compound having a morpholine structure and an oxygen functional group. A resist material comprising this amine compound has excellent resolution, but sometimes poor age stability. Compounds having aniline structure as described in Patent Documents 2 and 3 are known as the quencher providing relatively good shelf stability. Resist materials comprising these compounds still have insufficient resolution in micropatterning.